Industry has long used various types of switches and sensors for remote detection of many different conditions. For example, the linear variable displacement transducer uses the signal resulting from the electrical energization of a coil having a moveable ferrite core attached to a mechanical member to ascertain the position of the mechanical member. The failure modes in this typical sensing system are obvious. One or both of the energization wires to the coil could be severed. One or more of the sensing wires could be severed.
It would therefore be generically desirable to employ a switch or remote sensor having no electrical connection at the remote location. Due to the vibration and wear often occurring between the remote location and the device interpreting the signal from the sensor, it would be desirable to have a system which could withstand partial severance of the means with which the switch signal is transmitted.
One answer to this problem has been the use of a single fiber reflective switch sensing system. However, problems relating to interference from back reflections and scattering and the problems associated with light path discontinuities have made the present methods still less than ideal in meeting the needs of the industry.